In seismic exploration, scientists and engineers conduct “surveys” utilizing, among other things, seismic and other wave exploration techniques to find oil and gas reservoirs within the Earth. These seismic exploration techniques often include controlling the emission of seismic energy with a seismic source of energy (e.g., dynamite, air guns, vibrators, etc.), and monitoring the Earth's response to the seismic source with one or more receivers (e.g., geophones, hydrophones, accelerometers, etc.). By observing the reflected seismic signals detected by the receiver(s) during the survey, the geophysical data pertaining to reflected signals may be acquired, and these signals may be used to help create an image of the subsurface of the Earth and/or to indicate the composition of the Earth proximate to the survey location.
Geophysical exploration surveys are often conducted over large areas of land or water, often tens, hundreds, or even thousands of square miles. Traditionally, marine surveys are conducted in a “racetrack” manner, where a vessel acquires seismic data in relatively straight sail lines that allow the vessel to cover the most area in the least amount of time.
For example, FIG. 1A shows a plan view of a vessel 101 towing a source 102 and several receivers 103 on streamers 110 behind the vessel 101, and FIG. 1B shows a side-view of the vessel 101 shown in FIG. 1A with the source 102 and receivers 103 being towed behind the vessel 101 beneath the surface of the water.
During operations, the source 102 emits or “fires” seismic energy (e.g., through an air gun), which may reflect off various portions of the Earth 104 and may be received back at the receivers 103 along the streamers 110. The signal received and processed at the receivers 103 may indicate the composition of various portions of the Earth 104 proximate the location where the signal was reflected, for example an oil and/or gas reservoir 105.
FIG. 2 is a plan view of a vessel 201 acquiring seismic data in a “racetrack” manner mentioned above. The seismic data may be acquired along sail lines, each of which may be a planned course for the vessel 201 to travel along. Sail lines may in some cases be referred to as lines, tracks, or sequences; alternatively, in some cases, sequence may refer to the seismic data recorded during acquisition when the vessel 201 travels substantially along a sail line.
Completed lines (e.g., lines along which seismic data has already been acquired) are indicated in bold in FIG. 2, whereas potential candidate lines are represented in FIG. 2 as long dashes. The vessel 201 may have initially acquired data along line 210 while traveling in a southbound direction, then turned left 180 degrees (as shown by the small dashes) and acquired data along line 211 while traveling in a northbound direction. Then, the vessel 201 may have turned left 180 degrees again and acquired seismic data along line 212.
After acquiring data along line 212, the vessel 201 may have many potential candidate lines along which to acquire seismic data, such as lines 220-224. In some instances, the vessel 201 may need to acquire infill data along a particular line 211 to infill incomplete or poor-quality data, for example.
Although the lines in FIG. 2 are relatively straight, it will be appreciated that the actual travel path of the vessel 201 may vary from the intended sail line. During acquisition, many factors impact the quality of the data that is acquired and the time that it takes to acquire that data. For example, in the marine context, sea currents, bad weather, swell noise, seismic interference, other vessels in the area, equipment problems, and so forth may cause imperfections or anomalies in the acquired data. In some instances, data may not be collected at all for certain coordinates (because, for example, sea currents pushed a seismic receiver out of its intended path), or the data may have so much noise or other problems so as to be unusable.
In these cases, the holes in data coverage may need to be rectified by conducting “infill,” which may involve a repeat trip by a vessel to the same area. Conventional geophysical seismic surveys often cost thousands or tens of thousands of dollars per hour to complete so repeating the survey to infill data can be costly. Therefore, methods and apparatuses are desired that facilitate determination of locations to acquire data in order to increase the quality of data acquired and reduce costs associated with conducting the surveys.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.